Improve available output

The available command can now:

• differentiate between the toolchains and the package_sets
• show the packages that packages_sets have:

❯ ./mpsd-software-environment.py available dev-23a

MPSD software release dev-23a provides:
Toolchains: 
    foss2021a-cuda-mpi
    foss2021a-mpi
    foss2021a-serial
    foss2022a-cuda-mpi
    foss2022a-mpi
    foss2022a-serial
Package sets:
   global_generic ( anaconda3@2022.10 )  
   global ( octopus@12.1, octopus@12.1 )  

requested review from @hans.fangohr

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• f2d2be1d - update changes from upstream

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• 39f8590a - black

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added 4 commits

• 39f8590a...9be3627e - 3 commits from branch main
• 93c98403 - Merge branch 'main' into 'improve-available-cmd'

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• 119922fd - review and suggestions

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I made some suggestions and adjustments.

The output is not particularly machine readable, but perhaps that's not required; at least not now.

approved this merge request

merged

mentioned in commit 361193a6